Windows 8 will include its own built-in antivirus software. But if a user installs antivirus software from McAfee, Symantec, AVG, or any other vendor, Windows 8's own protection will turn itself off and defer entirely to the third-party product. Microsoft's software will spring to life only if there's no third-party malware protection at all or if the third-party software is installed but has no up-to-date signatures.

Representatives from McAfee spoke to Computerworld to explain the behavior. While this might seem like a concession from Microsoft to the third-party antivirus vendors, McAfee says it isn't. Rather, it's designed to keep Windows OEMs happy.

OEMs have long bundled third-party antivirus software with their systems, because they receive kickbacks from the antivirus vendors whenever users buy subscriptions to the software. Windows 8's built-in antivirus software threatened this revenue stream; if Windows offers to perform antivirus functionality all by itself, there's no reason to buy a subscription.

Windows 8 will warn users when their antivirus software is out-of-date and provide them information on how to renew their subscription. After 15 days of warnings, it will also offer to install Microsoft's own Windows Defender. This combines the anti-spyware properties of Windows Defender and the antivirus capabilities of Microsoft Security Essentials.

Our advice would be to blow away the bloatware and skip the trials. Head straight for Microsoft's software. It's not perfect—no antivirus software is—but it keeps a low profile and will protect against all the mainstream malware threats.